Dispersion of bare nanoparticles in nonpolar solvents

ABSTRACT

Methods are disclosed for dispersing nanoparticles in solvents, involving the use of a cationic species and an anionic species, where at least one of the ionic species is soluble in the nonpolar solvent and the other ionic species has a relatively strong affinity for the surface of the nanoparticles. The cationic species and the anionic species together form a cluster of ion pairs shielding the nanoparticles and enhancing their dispersibility in the nonpolar solvent.

FIELD OF THE INVENTION

Innovations are disclosed in the field of organic chemistry, related to dispersions of solid nanoparticles decorated with ionic species in nonpolar solvents.

BACKGROUND

Nonpolar solvents (e.g. toluene, hexanes, dodecanes, scCO₂, etc.) have very low dielectric constants. This leads to the absence of electric double layer and poor solvency of bare metal oxide nanoparticles in such solvents which make the nanoparticles non-dispersible in these media. Several methods are available to stabilize the nanoparticles in these solvents. Surface modification of nanoparticles using organic molecules can assist the stability in nonpolar solvents (Li and Zhu 2003). However, this method is not trivial and involved complex steps of covalently bonding such as esterification and amidization, and purification which is not feasible for scale up processes.

Nanoparticles dispersions in nonaqueous nonpolar media has gained a wide interest recently due to promising applications. While polymer adsorption on nanoparticles can sterically stabilize the dispersion, several applications need charged particles in nonpolar media. The importance of these charged dispersions is sensed in many fields such as liquid immersion development (LID), electrostatic lithography, drop-on-demand ink jet, photoelectrophoresis, electrophoretic displays, and electrorheological fluids (Morrison 1993, Comiskey et al. 1998, Hao 2001, Sainis et al. 2008). Other applications that require electrostatic repulsions such as prevention of asphaltene precipitation in oil reservoirs (Leon et al. 1999), dispersion of nanoparticles in scCO₂ (Ryoo et al. 2006), and stabilization of particles for airborne drug delivery (Jones et al. 2006).

Provided a comprehensive literature review of the electrical charges in nonaqueous media along with the key applications of such dispersions. In general particles charge is due to either specific adsorption of ions from the solution or dissociation of the groups on the surface of the particles. Existence of water even in very low content in the nonpolar solvents can significantly affect the charging of the particles as it affects the formation ions structures and the surface chemistry of the particles.

Poovarodom and Berg (2010) studied the effect of acid-base properties on charging of colloids in apolar media. In their study the nanoparticles were initially surface functionalized with either acid or base and then dispersed in apolar solvents that contains either acid or base surfactants. They found that at high enough surfactant concentration (above the critical micelle concentration) the nanoparticles can be charged. Both the polarity and magnitude of the surface charge are found to depend strongly on the acid-base properties of the surface and the surfactant.

SUMMARY

A facile method is provided for stabilizing nanoparticles in nonpolar solvents. The method involves using an ion complex of an acid and a base to stabilize nanoparticles, including bare nanoparticles that do not have any covalently bonded surface molecules. The ions are selected to have a mutual solubility in the targeted nonpolar solvent to act as a bridge between the nanoparticles and the solvent. The method involves using two different molecules: cation and anion, where at least one of them is soluble with the target nonpolar solvent and the other one has strong affinity for the surface of the nanoparticles. Both molecules, the cation and the anion, together form a cluster of ion pairs shielding the nanoparticles and enhancing their dispersibility on the target nonpolar solvent. In this way, interactions between the surface of the nanoparticles and surface-associated ion pairs provides a degree of stabilization.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 includes two line graphs, illustrating the results of viscosity measurements of samples 58, 59, and 60 with 1.0 wt % of IL2 and various wt % of Aerosil-200 (58-1.0, 59-2.0, 60-4.0) after sonication (left) and after 1 week (right).

FIG. 2 includes two line graphs, illustrating the results of viscosity measurements of samples 122, 127, and 128 with 1.0 wt % IL1 and different wt % of Aerosil-200 (122-1.0, 127-2.0, 128-3.0), (left) after sonication, and (right) after 1 week.

FIG. 3 includes two line graphs, illustrating the results of viscosity measurements of samples 123, 129, and 130 with 1.0 wt % IL3 and different wt % of Aerosil-200 (123-1.0, 129-2.0, 130-3.0), (left) after sonication, and (right) after 1 week.

FIG. 4 is a line graph, illustrating the results of viscosity measurements of samples 62 (1.0 wt % Aerosil-200) and 63 (2.0 wt % Aerosil-200), both with 1.0 wt % of IL5.

FIG. 5 is a line graph, illustrating the results of viscosity measurements of samples containing different ratios of IL2:dodecane (140-10:90, 141-20:80, 142-30:70, 143-40:60) prior to the addition of Aerosil-200.

FIG. 6 is a line graph, illustrating the results of viscosity measurements of samples containing 8.0 wt % Aerosil-200 with different ratios of IL2:dodecane (140-10:90, 141-20:80, 142-30:70, 143-40:60) after sonication.

FIG. 7 is a line graph, illustrating the results of viscosity measurements of samples containing 8.0 wt % Aerosil-200 with different ratios of IL2:dodecane (140-10:90, 141-20:80, 142-30:70, 143-40:60) after 1 week.

FIG. 8 is a line graph, illustrating the results of viscosity measurements of samples containing 1.0 wt % mixture of Octylamine and Oleic Acid (1:1 M) AB1 with different Aerosil-200 wt % (126-1.0 wt %, 135-2.0 wt %, and 136-4.0 wt %) after 1 week.

FIG. 9 includes three bar graphs, illustrating the percentage Fe₃O₄ remaining in (a) samples 74-89 containing IL2, IL5, and IL6 at 1.0-5.0 wt % sonicated for 10 minutes, (b) samples 90-105 containing IL2, IL5, and IL6 at 1.0-5.0 wt % sonicated for 30 minutes, and (c) samples 106-121 containing IL2, IL5, and IL6 at 1.0-5.0 wt % sonicated for 60 minutes.

FIG. 10 is a line graph illustrating the mobility of AluC Coated with IL2 in dodecane (1 wt % AluC).

FIG. 11 is a line graph illustrating the mobility of AluC Coated with IL6 in dodecane (1 wt % AluC).

FIG. 12 is a photograph of samples with different concentrations of IL2 with carbon black in dodecane after 1 week, AS58 (1 wt %), AS60 (0.5 wt %), AS61 (0.1 wt %), AS62 (0.05 wt %) and AS59 (0 wt %) (Photo took after two days of sonication).

DETAILED DESCRIPTION

One general aspect of the methods disclosed herein includes a method for stabilizing a dispersion of nanoparticles in a nonpolar solvent, including admixing with the nanoparticles in the solvent stabilizing amounts of an anionic species and a cationic species that together form ionic or hydrogen bonds therebetween in the dispersion, where a first one of the anionic or the cationic species has a higher relative affinity for the nanoparticles in the solvent, and the other of the anionic or cationic species has a greater relative solubility in the nonpolar solvent than the first ionic species. The method also includes where the cationic species and the anionic species are each separately soluble in the non-polar solvent in the stabilizing amounts, or the anionic and cationic species are together capable of forming an ionic compound that is soluble in the non-polar solvent to provide the anionic and cationic species in the stabilizing amounts; and. The method also includes where the dispersion is formed into a stable non-precipitating dispersion of the nanoparticles in the presence of the anionic and cationic species in the nonpolar solvent, under stabilized conditions for a stabilized period of time where, in the absence of the anionic and the cationic species, the nanoparticles would precipitate under the stabilized conditions within the stabilized period of time.

Implementations may include one or more of the following features. The method where the ionic compound is an ionic liquid at a temperature at which the dispersion is stabilized, or under the stabilized conditions. The method where the ionic liquid has a melting point below 200° C. The method where the ionic liquid includes a primary, secondary, tertiary or cyclic amine. The method where the ionic liquid includes a primary, secondary or tertiary alkyl amine. The method where the ionic liquid includes one or more primary carboxylic acid, saturated or unsaturated. The method where the ionic liquid includes one or more primary sulfonic acid, saturated or unsaturated, such as an alkyl sulfonic acid. The method where the ionic liquid includes one or more primary, saturated or unsaturated alkyl benzene sulfonic acid. The method where the ionic liquid is butylammonium oleate, N-octylammonium oleate, tri-ethylammonium oleate, tri-N-butylammonium oleate, or tri-N-octylammonium oleate, butylammonium dodecyl benzenesulfonate, n-octylammonium dodecyl benzenesulfonate, tri-ethylammonium dodecyl benzenesulfonate, tri-n-butylammonium dodecyl benzenesulfonate, tri-n-octylammonium dodecyl benzenesulfonate. The method where the nonpolar solvent has a dielectric constant of less than 15. The method where the stabilized conditions include an average or maximum gravitational force during the stabilized period of 1 gravity and an ambient temperature or a temperature above a freezing point or below a boiling point of the dispersion. The method where the nanoparticles include a nanoparticle is included substantially of a metal, a metalloid, a metal oxide, a metalloid oxide, carbon, cellulose or a mixture thereof. The method where the metal or metaloid oxide includes silicon oxide, iron oxide or aluminium oxide; the carbon includes carbon black or carbon nanotubes; or, the cellulose includes cellulose nanocrystals. The method where the nanoparticles include a nanoparticle including an element selected from the group including of Fe, Al, Ag, Au, Co, Mo, N, Ni, Pd, Pt, S, Sn, Si, Ti, W, or Zn. The method where the nanoparticles have an average dimension ranging from 1 nm to 1000 nm. The method where the nanoparticles include a nanoparticle that has a charged particle surface in the dispersion. The method where the charged surface is positively charged. The method where the charged surface is negatively charged. The method where the nanoparticles include a nanoparticle that does not have a charged particle surface in the dispersion. The method where the stabilization period is 1 day, 1 week, 1 month or 1 year. The method where the nanoparticles are present in the dispersion in an amount ranging from 0.0001 wt. % to 50 wt. % relative to the dispersion weight (for example being greater than 0.0001 wt. %, 0.001 wt. %, 0.01 wt. %, 0.1 wt. %, 1 wt. %, 10 wt. %, 20 wt. %, or 30 wt. % and/or less than 50 wt. %, 40 wt. %, 30 wt. %, 20 wt. %, 10 wt. %, 1 wt. %, 0.1 wt. % or 0.01 wt. %, or any range between any two of these lower and upper amounts). The method where a weight ratio of the combined anionic and cationic species to the nanoparticles in the dispersion ranges from 1:10 to 10:1 combined species to nanoparticles (for example being about 1:10, 1:9, 1:8, 1:7, 1:6, 1:5, 1:4, 1:3, 1:2, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1 or 10:1, or in any range between any two of these ratios). The stable non-precipitating dispersion of the nanoparticles in the presence of the anionic and cationic species in the nonpolar solvent, made according to the method.

One general aspect includes a stable dispersion of nanoparticles in the presence of anionic species and cationic species in a nonpolar solvent, where the anionic and cationic species are present in solvent stabilizing amounts and together form ionic or hydrogen bonds therebetween in the dispersion, where a first one of the anionic or the cationic species has a higher relative affinity for the nanoparticles in the solvent, and the other of the anionic or cationic species has a greater relative solubility in the nonpolar solvent than the first ionic species. The stable dispersion of nanoparticles also includes where the cationic species and the anionic species are each separately soluble in the non-polar solvent in the stabilizing amounts, or the anionic and cationic species are together capable of forming an ionic compound that is soluble in the non-polar solvent to provide the anionic and cationic species in the stabilizing amounts; and. The stable dispersion of nanoparticles also includes where the stable dispersion is non-precipitating under stabilized conditions for a stabilized period of time where, in the absence of the anionic and the cationic species, the nanoparticles would precipitate under the stabilized conditions within the stabilized period of time.

Aspects of the disclosed processes include processes having a single stabilization step that provides a stable dispersion, with no solvent transfer, heat or complex chemical reactions required. These ADL methods may accordingly be adapted for applications such as: water-in-oil emulsions in the food industry; water-in-oil emulsions for drilling fluids; nonaqueous foams; dispersion of Graphene oxides; liquid immersion development (LID); electrostatic lithography; drop-on-demand ink jet; photoelectrophoresis; electrophoretic displays; or electrorheological fluids.

Although various embodiments of the invention are disclosed herein, many adaptations and modifications may be made within the scope of the invention in accordance with the common general knowledge of those skilled in this art. Such modifications include the substitution of known equivalents for any aspect of the invention in order to achieve the same result in substantially the same way. Numeric ranges are inclusive of the numbers defining the range. The word “comprising” is used herein as an open-ended term, substantially equivalent to the phrase “including, but not limited to”, and the word “comprises” has a corresponding meaning. As used herein, the singular forms “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a thing” includes more than one such thing. Citation of references herein is not an admission that such references are prior art to the present invention. Any priority document(s) and all publications, including but not limited to patents and patent applications, cited in this specification are incorporated herein by reference as if each individual publication were specifically and individually indicated to be incorporated by reference herein and as though fully set forth herein. The invention includes all embodiments and variations substantially as hereinbefore described and with reference to the examples and drawings.

Examples

The following Example relate generally to the formation of stable dispersions in non-aqueous liquid medium of nanoparticles such as carbon-based nanoparticles, inorganic nanoparticles, and organic nanoparticles by direct addition of the nanoparticles and the ionic liquid stabilizer to the desired solvent.

Materials and Methods

N-decylamine, N-butylamine, N-octylamine, tri-N-butyl-amine, tri-N-octylamine, and N,N′-Dimethyl-1,3-propanediamine were purchased from TCI chemicals. Iso stearic acid was obtained from TCI chemicals. Oleic acid was obtained as a technical grade. All the chemicals were used without further purification.

Ionic Liquids (ILs) were synthesized using the procedure discussed elsewhere (McCrary et al. 2013). ILs were synthesized first by mixing the bulk base and acid. While acid-base solutions (Abs) were made by directly adding the acid and base in any order into the nonpolar solvents. The molar ratio of the base-to-acid is 10:1, 5:1, 1:1, 1:5, or 10:1. Three different oxide nanoparticles were used. Aerosil-200 Fumed silica and Aeroxide Alu C nanoparticles were purchased from Evonik. Iron oxide nanoparticles were obtained from SkySpring. The nanoparticles were in powder form. Carbon black (Vulcan-XC-72R), non-oxide nanoparticles, was obtained from Cabot. Carbon nanotubes were obtained from Cheap Tubes Inc.

TABLE 1 Structure of ionic liquids used in this study Chemical # Full Name Formula IL1 Butylammonium oleate [C₄NH₃][oleate] IL2 N-octylammonium oleate [C₈NH₃][oleate] IL3 N-dodecylammonium oleate [C₁₂NH₃][Oleate] IL4 Tri-ethylammonium oleate [HN₂₂₂][oleate] IL5 Tri-N-butylammonium oleate [HN₄₄₄][oleate] IL6 Tri-N-octylammonium oleate [HN₈₈₈][oleate] IL7 N-octylammonium dodecyl [C₈NH₃][DBS] benzenesulfonate AB1 N-octylamine/oleic acid(1:1M) AB2 N,N′-Dimethyl-1,3- propanediamine/Iso-Stearic acid (1:1M)

In order to stabilize the nanoparticles in nonpolar solvents, these examples illustrate a variety of embodiments that make use of different acids, bases, and mixtures of acids and bases, in the form of either ILs or ABs. The ILs were diluted in the nonpolar organic solvents. In case of ABs, the acid and base were added individually and directly to the nonpolar organic solvents. Moreover, the acid and base were tested individually and tested for their efficiency of stabilized bare nanoparticles in nonpolar organic solvents. Then the nanoparticles were added, and the solutions were sonicated for 2 minutes using ultrasonication probe. The following procedure was used to prepare the nanoparticles dispersions in nonpolar solvents.

A mixture of dodecane (in some case, N-Hexane was used) with a specified wt % of the reagent was stirred for 30 minutes (500-700 rpm) with a magnetic stirrer. A funnel was used to add nanoparticles to the solution while stirring at high speed (1000 rpm). The stir bar used was small and flat in order to avoid the formation of a vortex at the meniscus of the solution which could cause particles to shoot up and collect on the edges of the vial. The mixture was then sonicated for 2 minutes (30 sec. on, 30 sec off) with an ultrasonication probe (420-A micro-tip) at 50% amplitude. The vial was grounded in an ice bath during sonication.

Photographs of the samples were taken, and visual observations were recorded at different time intervals. The particle size distribution (PSD) was measured using DLS with glass cuvette at different time intervals. Viscosity was measured using concentric cylinders viscometer (16 mL cylinder holder with ULA spindle). Particle size distribution of the nanoparticles was then measured using dynamic light scattering (DLS) with NanoPlus HD instrument. Viscosity measurements were conducted using Brookfield DV2T viscometer. ICP-MS triple quad was used to determine the concentration of iron oxide in the supernatants. The Fe₃O₄ was first digested using nitric acid at 90° C. before injecting it into the ICP-MS.

Results and Discussions Dispersion of Aerosil-200 Fumed Silica Nanoparticles in Dodecane Acids

In this section, two different organic acids; oleic acid and iso-stearic acids were tested for their effect on bare silica nanoparticles stability in dodecane. Aerosil-200 Fumed Silica nanoparticles dispersions in dodecane without organic acids are unstable. Without addition of any stabilizer, at low concentrations of nanoparticles (1-2 wt %), flocculation was observed immediately after sonication. While at higher concentrations of nanoparticles (4-8 wt %), gelation was produced either during stirring (4 wt %) or during sonication (8 wt %).

With the addition of oleic acid or iso-stearic acids, at low concentrations of nanoparticles, stability was improved slightly for the first 2-3 hours. However, flocculation developed heavily afterwards. Samples with higher concentrations of nanoparticles also formed gels. Samples with 4 and 8 wt % nanoparticles gelled during stirring and sonication, respectively.

Table 2 shows the composition of the samples that were prepared, and their characterization based on visual observation after sonication and after 1 week of preparation.

TABLE 2 Effect of acids on the stability of nanoparticles in dodecane (After sonication) Aerosil- Reagent 200, Dodecane Visual Observation # Reagent wt % wt % wt % After sonication After 1 week DB46 None 0 1.0 99.0 Immediate Remained flocculated Flocculation DB47 None 0 2.0 98.0 Immediate Flocculation DB48 None 0 4.0 96.0 Gelling Remained Gelled (sonication) DB49 None 0 8.0 92.0 Gelling (stirring) Remained Gelled DB50 Oleic 1 1.0 98.0 Flocculation within Precipitated Acid 2-3 h DB51 Oleic 1 2.0 97.0 Immediate Precipitated Acid Flocculation DB52 Oleic 1 4.0 95.0 Gelling Remained Gelled Acid (sonication) DB53 Oleic 1 8.0 91.0 Gelling (stirring) Remained Gelled Acid DB54 Iso- 1 1.0 98.0 Flocculation 2-3 Precipitated stearic hrs Acid DB55 Iso- 1 2.0 97.0 Flocculation 2-3 Remained flocculated stearic hrs Acid DB56 Iso- 1 4.0 95.0 Gelling Remained Gelled stearic (sonication) Acid DB57 Iso- 1 8.0 91.0 Gelling (stirring) Remained Gelled stearic Acid

-   -   The particles size distribution (PSD) measurements were         performed on the samples presented in Table 2 right after         sonication and the PSD measurements repeated after 1 week, to         assess cumulative diameter and Polydispersity Index (PDI). As         shown below in Table 3, heavy flocculation was attained in all         the samples. These experiments show that a variety of organics         acids cannot stabilize silica nanoparticles in dodecane.

TABLE 3 PSD parameters for non-flocculated and non-gelled samples containing 1.0 wt % of reagents (Oleic Acid, Iso-stearic Acid) with various Aerosil-200 wt %. After sonication After 1 week Aerosil- Cumulative Cumulative Reagent 200 Diameter Diameter Sample Reagent wt % wt % (nm) PDI (nm) PDI DB51 Oleic Acid 1 2.0 3887.1 1.784 — — DB54 Iso-stearic 1 1.0 2863.7 1.754 — — Acid DB55 Iso-stearic 1 2.0 8738.3 2.54 — — Acid

Bases

In order to evaluate the effect of organic bases on the stability of nanoparticles in nonpolar solvents, two organic bases were tested. In this section, N-octylamine and N, N′-Dimethyl-1, 3-propanediamine were mixed with Aerosil-200 Fumed silica nanoparticles using the procedure explained previously. N-octylamine did not stabilize the nanoparticles in dodecane. While N-octylammonium acetate was not miscible in dodecane at ambient temperature. N, N′-Dimethyl-1, 3-propanediamine had similar performance to N-octylamine. As shown in Table 2, none of the bases tested could achieve long-term stability of the Aerosil-200 Fumed Silica nanoparticles dispersion in dodecane. However, the nanoparticles are more stable compared to the one without stabilizers or with acids. Table 4 shows the compositions of the samples tested in this section and their visual observation after sonications. As shown in the table, N, N′-Dimethyl-1,3-propanediamine is slightly efficient compared to N-octylamine.

The particles size distribution (PSD) measurements were performed on the sample with N-octylamine right after sonication. Heavy flocculation was attained in the sample. Table 5 shows the sonication and PSD parameters for samples containing various Octylamine at 1.0 wt % with 1 wt % Aerosil-200 wt %.

TABLE 4 Effect of bases on the stability of nanoparticles in dodecane (After sonication) Aerosil- Sample Reagent 200, Dodecane Visual Name Reagent wt % wt % wt % Observation DB124 N-octylamine 1 1.0 98 Immediate Flocculation DB131 N- 1 N/A 98 insoluble octylammonium Acetate N,N′-Dimethyl- 1 0.1 98.9 Flocculation 1,3- 2-3 hrs propanediamine N,N′-Dimethyl- 1  0.25 98.75 Flocculation 1,3- 2-3 hrs propanediamine

TABLE 5 Sonication and PSD parameters for samples containing various Octylamine at 1.0 wt % with 1 wt % Aerosil-200 wt %. Energy Cumulative Reagent Aerosil-200 Input Diameter Sample Reagent wt % wt % (J) (nm) PDI 124 Octylamine 1 1 3496 2375.9 1.385

Ionic Liquids (ILs)

In order to illustrate the present Artificial Double Layer (ADL) approach, several ILs were synthesized using the protocols referenced herein, and tested as follows. ILs of primary and tertiary amines combined with oleic acid were tested. The acids and bases for these ILs were tested in the previous sub-sections, and none of them could stabilize Aerosil-200 Fumed Silica nanoparticles in dodecane.

However, primary amine-based ILs were able to stabilize Aerosil-200 Fumed Silica nanoparticles for long term. With 1 wt % of IL2, stable dispersions of Aerosil-200 Fumed Silica nanoparticles at concentrations of 1, 2, and 4 wt %. While for 6 and 8 wt % of Aerosil-200 Fumed Silica nanoparticles, the dispersion gelled during stirring or sonication. IL1 and IL3 with primary amine of shorter and longer alkyl chain, respectively, could stabilize the dispersions and gave similar performance to IL1.

IL5 and IL6 with tertiary amines were barely able to stabilize the dispersion for 2-3 hrs when heavy flocculation and separation of nanoparticles started. Even the samples with IL5 and IL6 formed gel during sonication at lower concentration of Aerosil-200 Fumed Silica nanoparticles (4 wt %) compared to 6 wt % of Aerosil-200 Fumed Silica nanoparticles in the presence of primary amine-based ILs.

It is concluded that the formation of ion pairs is more efficient in the case of primary-amines due to the availability of 2 hydrogen atoms attached to the highly electronegative nitrogen. Hence, primary amines can form an H-bond with themselves and with the acid, giving a more complex clusters of ions. While tertiary amines can form an H-bond only with the acid by sharing the lone pair of electrons on the highly electronegative nitrogen. Due to the absence of a hydrogen atom attached to the nitrogen, tertiary amines can't form hydrogen bonds with themselves.

Table 5 summarizes the composition of the samples prepared with different ILs and the visual observation of these samples after sonication and after 1 week. Samples containing 1.0 wt % ILL IL2 or IL3 were the only sample to not gel during sonication at 4.0 wt % of Aerosil-200. All samples gelled at 8.0 wt % and had bubbles trapped in the gel, with the control and Oleic Acid samples containing the most air bubbles. Both IL5 and IL6 samples at 1.0 wt % and 2.0 wt % had the Aerosil-200 falling out of solution by the end of the day, however, the IL5 samples (64 and 66) seemed to be separating at a faster rate than the IL4 samples.

TABLE 5 Screening of different ILs for their stabilization of nanoparticles in dodecane after sonication and after 1 week. Aerosil- Visual Observation Sample Reagent 200 wt Dodecane After After 1 Name Reagent wt % % wt % Sonication Week DB58 IL2 1 1.0 98.0 Dispersed Remained Translucent Dispersed DB59 IL2 1 2.0 97.0 Dispersed Remained Translucent- Dispersed Cloudy DB60 IL2 1 4.0 95.0 Dispersed Remained Cloud Dispersed DB132 IL2 1 6.0 93.0 Gelled Remained Opaque while Gelled stirring DB61 IL2 1 8.0 91.0 Gelled Remained Opaque during Gelled sonication DB125 IL2 2 8.0 90 Gelled Remained Opaque during Gelled sonication DB122 IL1 1 1.0 98 Dispersed Remained Translucent dispersed DB127 IL1 1 2.0 97 Dispersed Remained Translucent- dispersed Cloudy DB128 IL1 1 4.0 95 Dispersed Remained Cloud dispersed DB133 IL1 1 6.0 93 Gelled Remained Opaque during Gelled sonication DB123 IL3 1 1.0 98 Dispersed Remained Translucent dispersed DB129 IL3 1 2.0 97 Dispersed Remained Translucent- dispersed Cloudy DB130 IL3 1 4.0 95 Dispersed Remained Cloud dispersed DB134 IL3 1 6.0 93 Gelled Remained Opaque during Gelled sonication DB62 IL5 1 1.0 98.0 Flocculation Precipitated 2-3 hrs DB63 IL5 1 2.0 97.0 Flocculation Precipitated 2-3 hrs DB64 IL5 1 4.0 95.0 Gelled Remained Opaque during Gelled sonication DB65 IL5 1 8.0 91.0 Gelled Remained Opaque while Gelled stirring DB66 IL6 1 1.0 98.0 Flocculation Precipitated 2-3 hrs DB67 IL6 1 2.0 97.0 Flocculation Precipitated 2-3 hrs DB68 IL6 1 4.0 95.0 Gelled Remained Opaque during Gelled sonication DB69 IL6 1 8.0 91.0 Gelled Remained Opaque while Gelled stirring

Although the diameter and PDI of the IL6 samples (66 and 67) indicates that they would be more stable than the IL5 samples (62 and 63), visual observation of precipitation do not agree. The phase separation may be due to the increased hydrophobicity of IL6 compared to IL5 due to base alkyl chain length. The base may be more prone to the organic phase and is not interaction through H-bonding with silanol groups on Aerosil-200, resulting in a separation of two phases: organic phase with dodecane and IL, and Aerosil-200 as precipitate.

New samples were prepared to test the dispersion of IL5 and IL6 at 1.0 and 2.0 wt % of Aerosil-200. These specific concentrations saw precipitation of the Aerosil-200 hours after sonication on the day of their preparation. Although PSD measurements of these samples align with previous trials done with IL5 and IL6 using 1.0 wt % of Aerosil-200, a previous trial done with IL5 and 1.0 wt % Aerosil-200 did not begin to separate until till after 10 days. The following samples were prepared:

TABLE 6 Composition of repeated IL4 and IL5 samples Sample Reagent Aerosil- Dodecane Name (1.0 wt %) 200 wt % wt % DB70 IL5 1.0 98.0 DB71 IL5 2.0 97.0 DB72 IL6 1.0 98.0 DB73 IL6 2.0 97.0

These samples also saw quick separation due to precipitation hours after initial sonication, and pictures were re-taken 24 hours after sonication. The IL6 samples experiences much more rapid separation as compared to the IL5 samples. The cumulative diameter and larger PDI of the IL6 samples compared to the IL5 samples agrees with the faster separation that was observed after 24 hours. The following are PSD measurements that were taken immediately after sonication.

TABLE 7 Visual observations of repeated IL5 and IL6 samples Aerosil- Reagent 200 Dodecane Visual Sample Reagent wt % wt % wt % Observation DB70 IL5 1 1.0 98 Phase Separated, Clear Upper, Opaque Bottom DB71 IL5 1 2.0 98 Phase Separated, Clear Upper, Opaque Bottom DB72 IL6 1 1.0 98 Phase Separated, Clear Upper, Opaque Bottom DB73 IL6 1 2.0 98 Phase Separated, Clear Upper, Opaque Bottom

PSD results were also obtained for many samples, but some samples were too heavily flocculated or gelled to obtain reliable results. Table 8 shows the PSD parameters of ILs samples with Aerosil-200 after sonication and after 1 week.

TABLE 8 PSD parameters of ILs samples with Aerosil- 200 after sonication and after 1 week. After sonication After 1 week Aerosil-200 Cumulative Cumulative Reagent Concentration Diameter Diameter Sample Reagent wt % (wt %) (nm) PDI (nm) PDI DB58 IL1 1 1.0 194.9 0.105 189.5 0.093 DB59 IL1 1 2.0 210.1 0.147 209.7 0.128 DB60 IL2 1 4.0 222.5 0.157 218.7 0.158 DB132 IL2 1 6.0 — — — — DB61 IL2 1 8.0 — — — — DB125 IL2 2 8.0 — — — — DB122 IL1 1 1.0 204.5 0.131 205.4 0.139 DB127 IL1 1 2.0 222.9 0.186 210.9 0.128 DB128 IL1 1 4.0 233.6 0.192 232.2 0.171 DB133 IL1 1 6.0 — — — — DB123 IL3 1 1.0 204.2 0.142 196.5 0.139 DB129 IL3 1 2.0 198.4 0.16 207.5 0.166 DB130 IL3 1 4.0 230.9 0.168 224.6 0.163 DB134 IL3 1 6.0 — — — — DB70 IL5 1 1.0 927.4 0.585 — — DB71 IL5 1 2.0 1154 0.721 — — DB64 IL5 1 4.0 — — — — DB65 IL5 1 8.0 — — — — DB72 IL6 1 1.0 742.1 0.496 — — DB73 IL6 1 2.0 591.9 0.427 — — DB68 IL6 1 4.0 — — — — DB69 IL6 1 8.0 — — — —

Viscosity measurements were also conducted. However, their validity needs to be re-assessed, and a suitable control needs to be decided. The control samples with only Aerosil-200 had a very low sample recovery from the viscometer due to the previously mention viscous fluid on the walls of the vials. Dodecane itself may serve as a better control test for viscosity.

Viscosity measurement of the IL2 samples indicate that the samples remained Newtonian after one week (FIG. 1 ). For the measurements, a 16 mL cylinder was used with a ULA spindle, and all measurements had torque between 10-100% with minimum speeds ranging from 40-50 rpm and the maximum speed set at 100 rpm for all samples. Viscosity measurements were taken for all the IL1 and IL3 samples using a 16 mL cylinder and ULA spindle. All measurements were taken using RPM's ranging from 40-100, all between 10-100% torque Increases in viscosity for samples using IL1 were greater for 1.0, 2.0, and 4.0 wt % Aerosil-200 compared to sample made using IL1 or IL3 from this week. However, viscosity increases IL1 and IL3 were almost identical at all well-dispersed concentrations of Aerosil-200 as seen in FIGS. 2 and 3 .

FIG. 4 shows the Viscosity measurements of samples 62 (1.0 wt % Aerosil-200) and 63 (2.0 wt % Aerosil-200), both with 1.0 wt % of ILS. As shown the samples are highly viscous and shear thinning indicating the growth of nanoparticles structures in the solutions

High Concentration of IL2

Previously, 8.0 wt % Aerosil-200 Fumed Silica nanoparticles in solution formed gels for all samples containing IL1, IL2, and IL3. Therefore, samples with a higher weight ratio between IL2 and dodecane were prepared to see if it was possible to disperse 8.0 wt % Aerosil-200 Fumed Silica nanoparticles without gelation. All higher concentration (>10 wt % of IL2) were able to stabilize the Aerosil-200 Fumed Silica nanoparticles and the condition of samples prepared are summarized below (Table 9).

TABLE 9 Weight fractions and state of samples 138- 143 after sonication and after 1 week. Aerosil-200 Weight wt % in Visual Observation Sample Fraction of Dodecane-IL After After Name Reagent IL1:Dodecane mixture sonication 1 Week DB140 IL2 10:90 8.0 Dispersed Remained dispersed DB141 IL2 20:80 8.0 Dispersed Remained dispersed DB142 IL2 30:70 8.0 Dispersed Remained dispersed DB143 IL2 40:60 8.0 Dispersed Remained dispersed DB138 IL2 50:50 8.0 Dispersed Remained dispersed DB139 IL2 50:50 8.0 Dispersed Remained dispersed

The PSD for samples 140, 141, and 142 (10:90, 20:80, and 30:70 of IL2:dodecane, respectively) which all contained 8.0 wt % Aerosil-200 displayed two peaks in their distributions. The first peak centered on a smaller diameter (<100 nm) for all three of these samples did not make up a significant part of either the intensity or volume distributions but had a larger percentage of the number distributions. Sample 143 (40:60 of IL2:dodecane), also containing 8.0 wt % Aerosil-200, did not display this behavior with its PSD as it only had a single peak. The peaks in the range <100 nm more likely belongs to the micelles of IL2. In comparison to the PSD measured after sonication, samples 140-142 did not display the secondary peaks seen in the intensity, volume, and number distributions after 1 week. The PDI and cumulative diameter also indicate smaller hydrodynamic diameters and more monodisperse particles after 1 week. Table 10 shows the sonication and PSD parameters for samples 140-143 containing 8.0 wt % Aerosil-200 with different ratios of IL2:dodecane after sonication and after 1 week.

TABLE 10 Sonication and PSD parameters for samples 140-143 containing 8.0 wt % Aerosil- 200 with different ratios of IL1:dodecane after sonication and after 1 week. After sonication After 1 Week Weight of Energy Cumulative Cumulative Fraction Input Diameter Diameter Sample IL2:Dodecane (J) (nm) PDI (nm) PDI 140 10:90 4089 224.5 0.16 197.1 0.147 141 20:80 3918 276.6 0.173 216.5 0.11 142 30:70 4241 282 0.192 235.9 0.132 143 40:60 4353 237.4 0.121 198.3 0.162

In order to elucidate the micelles of IL2, PSD results were gathered for samples with only IL2 and dodecane with the same weight fractions used for samples 140-143. The samples were sonicated for 2 minutes consistent with samples 140-143. Table 11 shows the sonication and PSD parameters for samples 144-147 containing different ratios of IL2:dodecane. The PSD clearly displayed some micelle formations. The intensity distribution for samples 144-147 (10:90, 20:80, and 30:70 weight fraction of IL:dodecane, respectively) all followed similar trends with multiple peaks ranging from 100 nm to 100000 nm for the intensity distributions. However, only single peaks were seen for the volume distribution (around 40000 nm) and number distributions (around 20 nm). Once again, the 40:60 weight fraction of IL:dodecane (sample 147) was an outlier as it displayed no PSD peaks, indicating no micelle formation. Sample 143, which also had the same ratio of IL:dodecane as sample 147, did not display a secondary peak as seen in other samples.

TABLE 11 Sonication and PSD parameters for samples 144-147 containing different ratios of IL2:dodecane. Weight Fraction of Energy Input Cumulative Sample IL2:Dodecane (J) Diameter (nm) PDI 144 10:90 3692 796.4 0.591 145 20:80 3662 3356.8 1.79 146 30:70 3982 1752 1.022 147 40:60 4022 N/A N/A

Viscosity measurements for sample 140-143 were taken before and after the addition of Aerosil-200 as the concentration of IL2 was great enough in each sample to have an impact on the viscosity of the solution. The viscosity of the sample prior to the addition of NPs displayed a trend on increasing viscosity with increasing IL2 concentration and all samples had relatively constant viscosities with increasing shear rates (FIG. 5 ). However, after the addition of 8.0 wt % of Aerosil-200, each sample had a significant increase in viscosity, but also had slight shear thinning effects (FIG. 6 ). The degree of shear thinning increased with increasing concentration of IL2. Whether the samples are non-Newtonian or not will be summarized in next week's report by fitting the data to the power law. The viscosity of each samples 140-143 did not show significant change after 1 week and continue to be higher that dodecane or IL with dodecane alone (FIG. 7 ). The shear thinning effect observed in higher concentrations of IL2 are still seen. As the viscosity parameters for sample 140-143 were all greatly varying, they are summarized in Table 22. All viscosities were measured using a ULA spindle with a 16 mL holder and all torques ranged from 10-100%.

Acid-Base Solutions (ABs)

The ABs version of IL2 were also tested. The ABs of octylamine and oleic acid (1:1M) stabilized the nanoparticles dispersion as efficient as ILs.

Then the ABs of octylamine and oleic acid (1:1 M), AB1, was tested and compared to ILL As shown in table 12, AB1 shows a good stability as IL2. Suggested that ABs can be replacing ILs. This makes the process much easier and more straightforward as no need for ILs synthesis since ABs in this case do the same job. Another acid-base solution was tested to validate the universality of the ADL theory. As shown in Table 12, AB2 can efficiently disperse Aerosil-200 Fumed silica nanoparticles in n-Hexane. While neither the diamine nor the iso-stearic acid can stabilize the dispersion.

Table 14 shows the sonication and PSD parameters for sample 135 and 136 containing 1.0 wt % of 1:1 M Octylamine and Oleic Acid and different Aerosil-200 wt %. AB1 can stabilize the dispersion up to 4 wt % of Aerosil-200. While 6 wt % of Aerosil-200 formed gel the same fashion as for IL2.

FIG. 8 shows viscosity measurements of samples containing 1.0 wt % mixture of Octylamine and Oleic Acid (1:1 M) AB1 with different Aerosil-200 wt % (126-1.0 wt %, 135-2.0 wt %, and 136-4.0 wt %) after 1 week. As shown, no significant increase in viscosity indicating a stable nanoparticles dispersion.

Hence, neither the acid nor base individually can achieve stability of the dispersion. However, when mixed together either the form of ILs or ABs, long term stability of the dispersion can be achieved. It's hypothesized that the ion pairs of acid and base can achieve the stability by creating an “Artificial Double Layer (ADL)” of mixed clusters of acid an bases with overall charges of either positive and negative.

Dispersion of SkySpring Iron Oxide in Dodecane Ionic Liquids (ILs)

Previous trials showed the ability to effectively disperse up to 25% of Fe₃O₄ used after addition of IL5 and sonication for 1 hour with stability for over 3 months. The following procedure was run with different ILs (IL2, IL5 and IL6) at different concentrations (1.0, 2.0, 3.0, 4.0, and 5.0 wt %) as well as different sonication times (10 min, 30 min, and 1 hour):

Prepare a mixture of dodecane with a specified IL at various concentrations and stir for 30 minutes (anywhere from 500-700 rpm) with a magnetic stirrer;

-   -   Add 1 wt % of Fe₃O₄ to the solution and stir manually with a         glass rod for 30 seconds;     -   Sonicate for various times (30 sec. on, 30 sec off) with a 408-B         solid-tip at 50% amplitude in an ice bath;     -   Take pictures, and let sit for 24 hours to precipitate;     -   Recover supernatant after 24 hours; and,     -   Take pictures, and measure PSD and remaining Fe₃O₄ concentration         in supernatant using ICP-MS.

Table 15 provides the summary of the samples tested for stability of ss-Fe₃O₄ in dodecane using ILs with the type analysis done for these samples.

TABLE 15 Summary of the samples tested for stability of ss-Fe₃O₄ in dodecane using ILs Sample Sonication IL IL wt Dodecane Name Time (min.) Used % wt % Color Code 74 10 None — 99.0 Samples with ICP-MS and PSD results 75 IL2 1.0 98.0 Samples with ICP-MS and PSD results 76 IL2 2.0 97.0 Samples with ICP-MS and PSD results 77 IL2 3.0 96.0 Samples with ICP-MS and PSD results 78 IL2 4.0 95.0 Samples with ICP-MS and PSD results 79 IL2 5.0 94.0 Samples with ICP-MS and PSD results 80 IL5 1.0 98.0 Samples with ICP-MS and PSD results 81 IL5 2.0 97.0 Samples with ICP-MS and PSD results 82 IL5 3.0 96.0 Samples with ICP-MS and PSD results 83 IL5 4.0 95.0 Samples with ICP-MS and PSD results 84 IL5 5.0 94.0 Samples with ICP-MS and PSD results 85 IL6 1.0 98.0 Samples with only PSD results which had to be diluted prior to DLS use 86 IL6 2.0 97.0 Samples with only PSD results which had to be diluted prior to DLS use 87 IL6 3.0 96.0 Samples with only PSD results which had to be diluted prior to DLS use 88 IL6 4.0 95.0 Samples with only PSD results which had to be diluted prior to DLS use 89 IL6 5.0 94.0 Samples with only PSD results which had to be diluted prior to DLS use 90 30 None — 99.0 Samples with only PSD results which had to be diluted prior to DLS use 91 IL2 1.0 98.0 Samples with only PSD results which had to be diluted prior to DLS use 92 IL2 2.0 97.0 Samples with only PSD results which had to be diluted prior to DLS use 93 IL2 3.0 96.0 Samples with only PSD results which had to be diluted prior to DLS use 94 IL2 4.0 95.0 Samples with only PSD results which had to be diluted prior to DLS use 95 IL2 5.0 94.0 Samples with only PSD results which had to be diluted prior to DLS use 96 IL5 1.0 98.0 Samples with only PSD results which had to be diluted prior to DLS use 97 IL5 2.0 97.0 Samples with only PSD results 98 IL5 3.0 96.0 Samples with only PSD results 99 IL5 4.0 95.0 Samples with only PSD results 100 IL5 5.0 94.0 Samples with only PSD results 101 IL6 1.0 98.0 Samples with only PSD results 102 IL6 2.0 97.0 Samples with only PSD results 103 IL6 3.0 96.0 Samples with only PSD results which had to be diluted prior to DLS use 104 IL6 4.0 95.0 Samples with only PSD results 105 IL6 5.0 94.0 Samples with only PSD results which had to be diluted prior to DLS use 106 60 None — 99.0 Samples with only PSD results which had to be diluted prior to DLS use 107 IL2 1.0 98.0 Samples with only PSD results 108 IL2 2.0 97.0 Samples with only PSD results 109 IL2 3.0 96.0 Samples with only PSD results which had to be diluted prior to DLS use 110 IL2 4.0 95.0 Samples with only PSD results which had to be diluted prior to DLS use 111 IL2 5.0 94.0 Samples with only PSD results which had to be diluted prior to DLS use 112 IL5 1.0 98.0 Samples with only PSD results which had to be diluted prior to DLS use 113 IL5 2.0 97.0 Samples with only PSD results which had to be diluted prior to DLS use 114 IL5 3.0 96.0 Samples with only PSD results 115 IL5 4.0 95.0 Samples with only PSD results 116 IL5 5.0 94.0 Samples with only PSD results 117 IL6 1.0 98.0 Samples with only PSD results which had to be diluted prior to DLS use 118 IL6 2.0 97.0 Samples with only PSD results 119 IL6 3.0 96.0 Samples with only PSD results which had to be diluted prior to DLS use 120 IL6 4.0 95.0 Samples with only PSD results which had to be diluted prior to DLS use 121 IL6 5.0 94.0 Samples with only PSD results which had to be diluted prior to DLS use

Sonication Time 10 Minutes

Firstly, a set of samples were prepared with a fixed concentration of ss-Fe₃O₄ and variable concentration of different ILs. It is worth mentioning that ss-Fe₃O₄ is poorly synthesized nanoparticles and it is difficult to disperse it even in water. All the samples prepared displayed a precipitate and a stable supernatant. The supernatants showed good stability with all polydispersity indices being close to 0.2 and most cumulative diameter's being close to 60 nm. Sample 78 had a small PDI but the diameter was much larger than the other samples with the same IL which may be a results of the lower energy input during sonication. However, the other samples with energy inputs close to 14000 did not experience a change in diameter or PDI from other samples. So far, there is no strong discernable trend that indicates higher IL concentration leads to smaller PSD.

TABLE 16 Sonication and PSD parameters for samples 74-86. PSD results obtained from supernatants collected after 24 hours. Sample Sonication Energy Dilution Cumulative IL Time Input Concentration Diameter Sample IL wt % (min.) (J) (vol %) (nm) PDI 74 None 0 10 25664 — — — 75 IL2 1 14313 — 54.1 0.197 76 IL2 2 25292 — 59.5 0.209 77 IL2 3 14622 — 63.1 0.224 78 IL2 4 28386 — 60.8 0.187 79 IL2 5 25606 — 69.4 0.221 80 IL5 1 26213 — 63.6 0.203 81 IL5 2 25276 — 65.2 0.197 82 IL5 3 25225 — 68.6 0.223 83 IL5 4 24789 — 67.4 0.227 84 IL5 5 24242 — 81 0.185 85 IL6 1 25614 — 64.1 0.154 86 IL6 2 25665 — 64 0.156 87 IL6 3 26343 — 64.9 0.188 88 IL6 4 27360 — 66.4 0.197 89 IL6 5 27293 — 67.2 0.21

Sonication Time 30 Minutes

In order to increase the dispersibility of Fe₃O₄ the sonication time was increased to 30-minute. Several samples were prepared and tested suing PSD. After decanting, the supernatants of the samples sonicated for 30 minutes displayed a much darker color than those sonicated for 10 minutes. They also took on a red hue when held up to light, whereas the samples sonicated for 10 minutes appeared to be light amber colored.

Table 17 is a summary of the sonication and PSD conditions of the samples prepared. Some of the samples, particularly the ones that were sonicated for 30 minutes, had supernatants which were too concentrated to give an accurate measurement on the DLS. These samples were diluted based on vol % and their PSD measurements aligned with those taken previously (˜60 nm diameter and ˜0.2 PDI).

TABLE 17 Sonication and PSD parameters for 30 minute sonication samples 90-105 (with IL2, IL5, or IL6). Sample Sonication Energy Dilution Cumulative IL Time Input Concentration Diameter Sample IL wt % (min.) (J) (vol %) (nm) PDI 90 None 0 30 79319 — N/A N/A 91 IL2 1 79492 — 57.8 0.173 92 IL2 2 81761 — 59 0.176 93 IL2 3 79452 — 57.8 0.211 94 IL2 4   60000 * — 55.4 0.176 95 IL2 5 99603 — 59.9 0.176 96 IL5 1 48532 — 61.8 0.193 97 IL5 2 76675 33 63.2 0.182 98 IL5 3 79478 33 60.5 0.161 99 IL5 4 75907 33 66.2 0.22 100 IL5 5 76934 50 59.8 0.201 101 IL6 1 78609 50 60.5 0.178 102 IL6 2 78535 50 61.7 0.169 103 IL6 3 78732 — 63.7 0.185 104 IL6 4 78693 50 66.6 0.226 105 IL6 5 77496 — 63.1 0.174

Sonication Time 60 Minutes

Another set of samples were prepared but the sonication time was increased to 60 minutes. The control sample (DB106) was heavily precipitated after sonication and very similar to the control samples for the other sonication times (DB74 and DB90). All samples took on a dark black color after sonication. After decanting, the supernatants for all samples were a dark amber color.

The energy inputs for all samples sonication for 60 minutes was around 155000 J, and all samples had similar PSD results that align with previous trials as well (Table 18). Similar to the samples with 30 minutes sonication, some samples had to be diluted with dodecane before the DLS could accurately measure the PSD. The concentration of sample DB106 was too low to obtain a reliable PSD measurement.

TABLE 18 Sonication and PSD parameters for 60 minute sonication samples (IL2, IL5, or IL6) Sample Sonication Energy Dilution Cumulative IL Time Input Concentration Diameter Sample IL wt % (min.) (J) (vol %) (nm) PDI 106 None 0 60 154838 N/A N/A N/A 107 IL2 1 151225 50 57.2 0.172 108 IL2 2 152958 50 55.5 0.172 109 IL2 3 154193 — 58.6 0.175 110 IL2 4 155993 — 57.1 0.158 111 IL2 5 152862 — 60.9 0.205 112 IL5 1 153079 — 58.3 0.173 113 IL5 2 153699 — 59.5 0.172 114 IL5 3 156552 50 58.4 0.185 115 IL5 4 155271 50 58.6 0.186 116 IL5 5 155859 50 59.9 0.176 117 IL6 1 155238 — 58 0.158 118 IL6 2 156410 50 59.1 0.163 119 IL6 3 157297 — 61.9 0.173 120 IL6 4 155868 — 60.5 0.187 121 IL6 5 156943 50 62.3 0.215

Summary of ICP-MS Data for Different Sonication Time

The following table and figures summarize previous and recent the ICP-MS results obtained for all SkySpring Iron Oxide samples (74-121) prepared using the procedure explained earlier.

In order to determine the concentrations of Fe₃O₄ acid digestion was done on the supernatants, following by analysis of iron concentration using both hydrogen and helium gases through the ICP-MS. As shown in the table, the use of ILs significantly enhance the dispersibility of ss-Fe₃O₄. Compared to the control that does not have any stabilizer, nearly all the nanoparticles precipitated immediately after sonication. It is worth mentioning that ss-Fe₃O₄ purchased from SkySpring company is a poorly synthesized nanoparticles and this leads to very poor dispersibility even with the addition of ILs. However, comparing the samples with and without ILs, it is evident that the ILs addition significantly enhance the dispersibility of ss-Fe₃O₄. See Table 19 for 10 minutes sonication, Table 20 for 30 minutes sonication, and Table 21 for 60 minutes sonication, for a summary of the results. FIG. 9 shows the percentage Fe₃O₄ remaining in (a) samples 74-89 containing IL2, IL5, and IL6 at 1.0-5.0 wt % sonicated for 10 minutes, (b) samples 90-105 containing IL2, IL5, and IL6 at 1.0-5.0 wt % sonicated for 30 minutes, and (c) samples 106-121 containing IL2, IL5, and IL6 at 1.0-5.0 wt % sonicated for 60 minutes.

The following sample calculation using data from sample 75 (1.0 wt % IL2, sonicated for 10 minutes):

$\begin{matrix} {{{Fe}{mass}{fraction}} = \frac{M_{Fe_{3}O_{4}}}{3 \times M_{Fe}}} \\ {{{Fe}{mass}{fraction}} = \frac{231.5476g/{mol}}{167.55g/{mol}}} \\ {{{Fe}{mass}{fraction}} = 0.7236} \\ {\left\lbrack {Fe_{3}O_{4}} \right\rbrack = \frac{\lbrack{Fe}\rbrack}{{Fe}{mass}{fraction}}} \\ {\left\lbrack {Fe_{3}O_{4}} \right\rbrack = \frac{11{7.2}46{ppm}}{{0.7}236}} \\ {\left\lbrack {Fe_{3}O_{4}} \right\rbrack = {162.{ppm}}} \end{matrix}$

TABLE 19 ICP-MS data for concentration of Fe remaining in samples 74-121 with different concentrations of IL2, IL5, and IL6 at 1.0-5.0 wt %, sonicated for 10 minutes. Initial Supernatant Percentage Sonication Concentration Concentration Concentration Time IL of Fe₃O₄ of Fe₃O₄ Remaining Sample (min.) IL wt % (ppm) (ppm) (%) 74 10 None 0 7575.78 0.49 0.006 75 IL2 1 7585.87 162.03 2.14 76 IL2 2 7596.00 339.32 4.47 77 IL2 3 7606.17 126.82 1.67 78 IL2 4 7616.36 86.82 1.14 79 IL2 5 7626.58 280.12 3.67 80 IL5 1 7585.80 519.99 6.84 81 IL5 2 7595.87 297.59 3.92 82 IL5 3 7605.96 215.09 2.83 83 IL5 4 7616.08 275.19 3.61 84 IL5 5 7626.23 169.70 2.22 85 IL6 1 7585.37 391.12 5.16 86 IL6 2 7595.01 654.47 8.62 87 IL6 3 7604.67 873.27 11.48 88 IL6 4 7614.36 869.01 11.41 89 IL6 5 7624.07 715.24 9.38

TABLE 20 ICP-MS data for concentration of Fe remaining in samples 74-121 with different concentrations of IL2, IL5, and IL6 at 1.0-5.0 wt %, sonicated for 30 minutes. Initial Supernatant Percentage Sonication Concentration Concentration Concentration Time IL of Fe₃O₄ of Fe₃O₄ Remaining Sample (min.) IL wt % (ppm) (ppm) (%) 90 30 None 0 7575.78 0.69 0.009 91 IL2 1 7585.87 1432.52 18.88 92 IL2 2 7596.00 1558.74 20.52 93 IL2 3 7606.17 1075.77 14.14 94 IL2 4 7616.36 1302.99 17.11 95 IL2 5 7626.58 1331.61 17.46 96 IL5 1 7585.80 1117.09 14.73 97 IL5 2 7595.87 1072.89 14.12 98 IL5 3 7605.96 1401.52 18.43 99 IL5 4 7616.08 867.86 11.39 100 IL5 5 7626.23 1217.35 15.96 101 IL6 1 7585.37 1721.23 22.69 102 IL6 2 7595.01 1147.10 15.10 103 IL6 3 7604.67 983.22 12.93 104 IL6 4 7614.36 960.51 12.59 105 IL6 5 7624.07 958.05 12.57

TABLE 21 ICP-MS data for concentration of Fe remaining in samples 74-121 with different concentrations of IL2, IL5, and IL6 at 1.0-5.0 wt %, sonicated for 60 minutes. Initial Supernatant Percentage Sonication Concentration Concentration Concentration Time IL of Fe₃O₄ of Fe₃O₄ Remaining Sample (min.) IL wt % (ppm) (ppm) (%) 106 60 None 0 7575.78 1.88 0.02 107 IL2 1 7585.87 1942.54 25.61 108 IL2 2 7596.00 2115.05 27.84 109 IL2 3 7606.17 1149.07 15.11 110 IL2 4 7616.36 1473.28 19.34 111 IL2 5 7626.58 1276.02 16.73 112 IL5 1 7585.80 1587.61 20.93 113 IL5 2 7595.87 1228.65 16.17 114 IL5 3 7605.96 1197.89 15.75 115 IL5 4 7616.08 1391.82 18.27 116 IL5 5 7626.23 1460.13 19.15 117 IL6 1 7585.37 1451.92 19.14 118 IL6 2 7595.01 1748.22 23.02 119 IL6 3 7604.67 1044.164 13.73 120 IL6 4 7614.36 1269.35 16.67 121 IL6 5 7624.07 968.44 12.70

Dispersion of Aeroxide Alu C in Dodecane

The state of the dispersions of AluC in dodecane, from stable dispersion to agglomeration, with two different reagents (IL2, IL6) is needed to be studied in order to determine the mobility and the minimum dispersion ILs wt %. The difference between the two nanoparticles' behavior was also being investigated since they have different polarity and physical characteristics. The following revised procedure from last week was used:

-   -   1. Prepare a mixture of dodecane with IL2 and IL6 held at 1.0 wt         % and stir for minutes (anywhere from 500-700 rpm) with a         magnetic stirrer     -   2. Add a fixed concentration of AluC (1 wt %) to the solution         using a funnel and occasionally shaking     -   3. Sonicate for 5 minutes (30 sec. on, 30 sec off) with a 420-B         tip at 50% amplitude in an ice-water bath     -   4. Take pictures, measure PSD (quartz cuvette), and measure         average mobility of the particles (low conductivity cell in 2         ml)     -   5. Observe visually for a few days

All the samples were prepared of 15 grams (around 20 mL) in 30 mL beaker and sonicated with a solid tip probe (420B). It is worth mention that since the compositions of the samples are the same compared to Aerosil-200 samples, the same weight ratio was used for preparation. In addition, the sonication time was extended to 5 minutes in order to completely disperse the samples.

Table 22 shows the composition of the samples prepared with IL2 and Alu C in Dodecane along with the sonication energy. While Table 23 shows the composition of the samples prepared with IL6.

TABLE 22 Sample Composition with IL1, Alu C, and Dodecane Calculated Alu Alu Weighted Sonication Sample IL2, IL2 Weighted C, C Alu C Dodecane Weighted Energy Name wt % (g) IL2(g) wt % (g) (g) (g) Dodecane (J) AS34 5 0.8096 0.8094 1 0.15 0.1504 14.0404 14.0401 14059 AS35 1 0.1619 0.1622 1 0.15 0.1499 14.6881 14.6881 13855 AS36 0.5 0.081 0.0814 1 0.15 0.1502 14.769 14.7693 13310 AS37 0.1 0.0162 0.016 1 0.15 0.1505 14.8338 14.8338 13298 AS38 0.05 0.0081 0.0081 1 0.15 0.1498 14.8419 14.8418 14275 AS39 0.01 0.0016 0.0017 1 0.15 0.1502 14.8484 14.8487 13215

TABLE 23 Sample Composition with IL6, AluC, and Dodecane Calculated Weighted Sonication Sample IL6, IL6 Weighted AluC, AluC AluC Dodecane Weighted Energy Name wt % (g) IL6(g) wt % (g) (g) (g) Dodecane (J) AS40 5 0.7999 0.8001 1 0.15 0.1500 14.0501 14.0504 14162 AS41 1 0.1600 0.1598 1 0.15 0.1497 14.6900 16.6904 14231 AS42 0.5 0.0800 0.0799 1 0.15 0.1503 14.7700 14.7700 14350 AS43 0.1 0.0160 0.0165 1 0.15 0.1496 14.8340 14.8340 15999 AS44 0.05 0.0080 0.0081 1 0.15 0.1496 14.8420 14.8422 17206 AS45 0.01 0.0016 0.0015 1 0.15 0.1502 14.8484 148482 16093 In general, a longer sonication time means more sonication energy was input into the solution. The DLS measurement and visual observations were expected to be different from the Aerosil-200.

Visual Observations

Firstly, the samples were inspected visually after sonication and photographs were taken. For dispersions prepared with IL2, based on the visual observation, for sample AS38, AS39 there are white precipitations at the bottom of the vial (precipitated 10 minutes after sonication), there are also transparent solid that sticks on the wall of the vails in these samples. Samples are cloudier compared to the solution that was made from Aerosil-200, and they are considered as translucent solutions instead of transparent solutions (Aerosil-200). Table 24 provides a detailed discussion of the visual observations of the sample from AS34 to AS39.

TABLE 24 Visual observations of the sample from AS22 to AS27 Sample Name Visual Observations AS34 Low viscosity, could flow like dodecane solvent A yellowish color, translucent solution, the solution shows orange color under the light No precipitation after a few days of preparation AS35 Low viscosity, could flow like dodecane solvent A lighter yellowish color, translucent solution, the solution shows orange color under the light No precipitation after a few days of preparation AS36 Low viscosity, could flow like dodecane solvent Almost white color, translucent No precipitation after a few days of preparation AS37 Low viscosity, could flow like dodecane solvent A white color solution, translucent No precipitation after a few days of preparation AS38 More viscous than the dispersed samples more cloudy, AS39 the precipitations could be seen in the vail Clear separations of precipitates and solvents after 10 minutes of sonication.

For dispersions prepared with ILS, for sample AS43, AS44 and AS45 there are white precipitations at the bottom of the vial (precipitated 10 minutes after sonication), there are also transparent solid that sticks on the wall of the vails in these samples. Table 25 provides a detailed discussion of the visual observations of the sample from AS40 to AS45.

TABLE 25 Visual observations of the sample from AS28 to AS30. Sample Name Visual Observations AS40 Low viscosity, could flow like dodecane solvent A light yellowish color, translucent solution, the solution shows a light orange color under the light. Similar to AS35. No precipitation after a few days of preparation AS41 Low viscosity, could flow like dodecane solvent A white color solution, translucent No precipitation after a few days of preparation AS42 Low viscosity, could flow like dodecane solvent White color, translucent No precipitation after a few days of preparation AS43 More viscous than the dispersed samples AS44 more cloudy, the precipitations could be seen in AS45 the vail after the sonication Clear separations of precipitates and solvents after 10 minutes of sonication.

Sample AS40, AS41, and AS42 were expecting to be the dispersed sample, as there was no precipitations and solid-solvent separations among these samples. DLS measurement was used for these samples to prove the state of dispersion.

DLS Measurements

Based on the visual observation, DLS measurements were conducted for all the non-precipitated samples prepared with IL2. These samples were expected to be dispersed (Table 26). For the samples prepared with IL6 (AS40-AS45), the sample AS40-AS42 were not having observable precipitations or agglomeration after the sonication, whereas the other three samples were agglomerated after the sample sonication. (Table 27).

TABLE 26 DLS measurements for AluC dispersions in Dodecane using IL1 (AS34 to AS37) Cumulant Sample Diameter Polydispersity Name IL2 (wt %) (nm) index Mobility(cm²/Vs) AS34 5 183.300 0.192 −4.053E−06 AS35 1 159.400 0.160  4.246E−07 AS36 0.5 158.100 0.159 −3.082E−06 AS37 0.1 153.300 0.133 −6.647E−08

As expected, the samples AS33 to AS37 are dispersed. The samples have similar particle sizes, the average particle sizes are ranging from 150 to 183, with around 0.15 PDI. The cumulant diameter has a decreasing trend, this trend may result from IL2 concentration difference in samples; the samples that have higher ILs wt % require more energy to disperse the samples completely. Since the sonication times were the same, more concentrated samples would have a higher cumulant diameter.

Table 27 also shows a similar PSD decreasing trend as IL6 was used instead.

TABLE 27 DLS measurements for AluC dispersions in Dodecane using IL6 (AS40 to AS42) Cumulated Sample Diameter Polydispersity Name IL6 (wt %) (nm) Index Mobility(cm²/Vs) AS40 5 267.000 0.123 −1.330E−07 AS41 1 152.200 0.146 −8.657E−07 AS42 0.5 153.300 0.146 −7.480E−07

The PSD measurements were conducted for dispersed samples using IL1 (5 wt % to 0.1 wt %) & IL5 (5 wt % to 0.5 wt %), Alu C in dodecane.

Most strikingly, the minimum dispersion IL2 concentration for Alu C nanoparticles is lower than Aerosil-200 (between 0.1-0.05 wt % for Alu C), similar behavior was also being found from the samples that were prepared by IL6 (between 0.5-0.1 wt % for Alu C). Since a similar change was observed for both ILs samples, it is possible that the particle charge characteristic of the ILs and nanoparticles are the major factor for the dispersion of these samples. As for the differences between IL2 and IL6, there are more samples that are dispersed for IL2, this may result from the steric interactions of IL6. However, this might be the minor factor, since there is no huge difference for the minimum dispersion concertation for IL2 and IL6.

The sample with 5 wt % IL6 has a wider range of particle sizes, this may due to the high concentration of the IL6 used (5 wt %) in this sample, the sample may not be fully sonicated to form an identical particle size.

The mobility tests were focused on the dispersed samples, as the ILs differences, two separated graphs are used to investigate the mechanism of the solution. All experiments were conducted under source voltage of 45 mV.

The mobility graph (FIG. 10 ) has a general trend similar to the A-200, IL2 samples, as the 1 wt % sample has a different polarity compared to the other samples. The 1:1 wt % ratio of nanoparticle and IL2 has a polarity difference, more literature review is needed to prove this observation. It is also possible that the data collected is not accurate enough as the mobility test for the low conductivity solutions is not fully developed. In addition, the characteristic change regarding the sonicated samples may also affect the experiment result (viscosity, dielectric constant).

As for the samples that used IL6 as the coating chemicals (FIG. 11 ), the polarity remains the same. The mobility is expected to be closer to 0 when more IL6 is used; 1 wt % IL6 sample has the highest mobility.

It is worth mentioning that the sample that was put into the cell tends to change the polarity when the second trial is being conducted for the same exact sample. As a result, the same sample cannot be run twice continuously in the low conductivity cell for any other future experiments.

Dispersion of Carbon Black in Dodecane

Carbon black (Vulcan XC 72R from Cabot with 50 nm size) was tested in order to get some insight on whether the stabilizing theory with ILs is working non-oxide nanoparticles. The preparation of the samples AS 58 (1 wt % IL2), 59 (0 wt % IL2), 60 (0.5 wt % IL2), 61 (0.1 wt % IL2), and 62 (0.05 wt % IL2) have followed the same method that was used for Aerosil-200 and AluC; all these samples were sonicated in 2 minutes. The first two samples with 1 wt % (AS58) and 0 wt % (AS59) of IL2 were prepared respectively to investigate the behavior of carbon black, which determines whether the follow-up tests should be prepared within the range between 1 wt % and 0 wt % (IL2 concentration) or not. For this week, all the samples were prepared using the vails instead of the beakers. Following detailed procedure was followed for the preparation of these samples.

-   -   1. Prepare a mixture of dodecane with IL2 with different wt %         and stir for 5 minutes (anywhere from 500-700 rpm) with a         magnetic stirrer     -   2. Add a fixed concentration of carbon black (0.1 wt %) to the         solution using a funnel and occasionally shaking (wear face         masks during the weighting and adding process)     -   3. Sonicate for 2 minutes (30 sec. on, 30 sec off) with a 420-A         microprobe at 50% amplitude in an ice-water bath     -   4. Take pictures, measure PSD (quartz cuvette), and measure         average mobility of the particles (low conductivity cell in 2         ml)     -   5. Observe visually for a few days

Table 28 shows the composition of the samples prepared with IL2 and carbon black in Dodecane along with the sonication energy.

TABLE 28 Sample Composition with IL2, Carbon Black, and Dodecane Calculated Carbon Carbon Weighted Sonication Sample IL2, IL2 Weighted Black, Black Carbon Dodecane Weighted Energy Name wt % (g) IL2(g) wt % (g) Black (g) Dodecane (J) AS58 1 0.1619 0.1615 0.1 0.015 0.0152 14.8231 14.8234 4020 AS60 0.5 0.0810 0.0807 0.1 0.015 0.0152 14.9040 14.9042 3753 AS61 0.1 0.0162 0.0162 0.1 0.015 0.0154 14.9688 14.9694 3728 AS62 0.05 0.0081 0.0081 0.1 0.015 0.0146 14.9769 14.9769 3740 AS59 0 0.0000 0.0000 0.1 0.015 0.0153 14.9850 14.9850 3741

Visual Observations

FIG. 12 shows the photographs of samples with different concentrations of IL2 with carbon black in dodecane after 1 week, AS58 (1 wt %), AS60 (0.5 wt %), AS61 (0.1 wt %), AS62 (0.05 wt %) and AS59 (0 wt %) (Photo took after two days of sonication). The dispersion prepared with no IL2 added (AS59) was seen to separate and precipitate with 2 h after sonication. meanwhile, the samples prepared with different concentrations of IL2 did not show any separation for at least few days. Since it was hard to observe the precipitation and dispersion behaviors for these samples, the DLS tests were conducted for all the samples. Table 29 provides a detailed discussion of the visual observations of the sample from AS58 to AS62.

TABLE 29 Visual observations of the sample from AS58 to AS62 Sample Name Visual Observations AS58 Low viscosity, could flow like dodecane solvent A deep black color, opaque solution, the solution shows no transparency under light No precipitation after a few days of preparation AS60 Low viscosity, could flow like dodecane solvent AS61 Bigger deep black particles floating in the lighter AS62 black solution No precipitation after a few days of preparation Low viscosity, could flow like dodecane solvent No precipitation after a few days of preparation AS59 Different level of black color in different heights of the vail after sonication Clear separations of precipitates and solvents after 3 hours of sonication.

DLS Measurements

Based on the visual observation, DLS measurements were conducted for all the non-precipitated samples prepared with IL2, since the carbon black samples precipitations were hard to observe shortly after the sonication; all the samples were tested in order to prove whether the samples were dispersed or not (Table 30), however, sample AS59 was precipitated after the PSD test. It is worth mention that due to the opaque characteristic of the carbon black samples, the mobility test samples were diluted in 1 (original solution):9 (dodecane) volume ratio.

TABLE 30 DLS measurements for Carbon Black dispersions in Dodecane using IL2 (AS58 to AS62) Cumulant Polydis- Sample IL2 Diameter persity standard Name (wt %) (nm) index Mobility(cm²/Vs) deviation AS58 1 1723.9 0.382  2.034E−06 1.491E−05 AS60 0.5 1420.1 0.466 −2.115E−06 1.178E−05 AS61 0.1 1285.1 0.229 −7.257E−07 4.757E−06 AS62 0.05 1233.8 0.018 −2.078E−05 1.194E−04 AS59 0 4856 0.217  8.761E−07 1.435E−05

For the samples that have IL2, the cumulant diameters are decreasing as the wt % of IL1 is decreasing. For mobility tests, except the sample AS58 and AS59, all other samples have negative average mobility. In addition, the standard deviation data are all different. In general, the higher the mobility the higher the STD, which means the difference between each trail is higher for the samples that have higher mobility.

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What is claimed is:
 1. A stable dispersion of nanoparticles in the presence of anionic species and cationic species in a nonpolar solvent, wherein the anionic and cationic species are present in solvent stabilizing amounts, wherein the stabilizing amounts of the anionic species and the cationic species are such that the molar ratios of the anionic species and of the cationic species, respectively to the nanoparticles, are different, and wherein the anionic and cationic species together form ionic or hydrogen bonds therebetween in the dispersion, wherein a first one of the anionic or the cationic species has a higher relative affinity for the nanoparticles in the solvent, and the other of the anionic or cationic species has a greater relative solubility in the nonpolar solvent than the first ionic species; and wherein the anionic and cationic species are together capable of forming an ionic compound that is soluble in the non-polar solvent to provide the anionic and cationic species in the stabilizing amounts; and, wherein the stable dispersion is non-precipitating under stabilized conditions for a stabilized period of time wherein, in the absence of the anionic and the cationic species, the nanoparticles would precipitate under the stabilized conditions within the stabilized period of time; wherein the ionic compound is an ionic liquid at a temperature at which the dispersion is stabilized, or under the stabilized conditions; and, wherein the ionic liquid is N-butylammonium oleate ([C4NH3][oleate]), N-octylammonium oleate ([C8NH3][oleate]), tri-ethylammonium oleate ([HN222][oleate]), tri-N-butylammonium oleate ([HN444][oleate]), tri-N-octylammonium oleate ([HN888][oleate]), N-octylammonium dodecylbenzenesulfonate ([C8NH3][DBS]), butylammonium dodecyl benzenesulfonate, tri-ethylammonium dodecyl benzenesulfonate, tri-N-butylammonium dodecyl benzenesulfonate, or tri-N-octylammonium dodecyl benzenesulfonate.
 2. The stable dispersion of nanoparticles of claim 1, wherein the ionic liquid is N-butylammonium oleate ([C4NH3][oleate]).
 3. The stable dispersion of nanoparticles of claim 1, wherein the ionic liquid is N-octylammonium oleate ([C8NH3][oleate]).
 4. The stable dispersion of nanoparticles of claim 1, wherein the ionic liquid is tri-ethylammonium oleate ([HN222][oleate]).
 5. The stable dispersion of nanoparticles of claim 1, wherein the ionic liquid is tri-N-butylammonium oleate ([HN444][oleate]).
 6. The stable dispersion of nanoparticles of claim 1, wherein the ionic liquid is tri-N-octylammonium oleate ([HN888][oleate]).
 7. The stable dispersion of nanoparticles of claim 1, wherein the ionic liquid is N-octylammonium dodecylbenzenesulfonate ([C8NH3][DBS]), butylammonium dodecyl benzenesulfonate, tri-ethylammonium dodecyl benzenesulfonate, tri-N-butylammonium dodecyl benzenesulfonate or tri-N-octylammonium dodecyl benzenesulfonate.
 8. The stable dispersion of nanoparticles of claim 1, wherein the nonpolar solvent has a dielectric constant of less than
 15. 9. The stable dispersion of nanoparticles of claim 1, wherein the stabilized conditions comprise an average or maximum gravitational force during the stabilized period of 1 gravity and an ambient temperature or a temperature above a freezing point or below a boiling point of the dispersion.
 10. The stable dispersion of nanoparticles of claim 1, wherein the nanoparticles comprise a nanoparticle that is comprised substantially of a metal, a metalloid, a metal oxide, a metalloid oxide, carbon, cellulose or a mixture thereof.
 11. The stable dispersion of nanoparticles of claim 10, wherein the metal or metalloid oxide comprises silicon oxide, iron oxide or aluminum oxide; the carbon comprises carbon black or carbon nanotubes; or, the cellulose comprises cellulose nanocrystals.
 12. The stable dispersion of nanoparticles of claim 1, wherein the nanoparticles comprise a nanoparticle comprising an element selected from the group consisting of Fe, Al, Ag, Au, Co, Mo, N, Ni, Pd, Pt, S, Sn, Si, Ti, W, or Zn.
 13. The stable dispersion of nanoparticles of claim 1, wherein the nanoparticles have an average dimension ranging from 1 nm to 100 nm.
 14. The stable dispersion of nanoparticles of claim 1, wherein the nanoparticles comprise a nanoparticle that has a charged particle surface in the dispersion.
 15. The stable dispersion of nanoparticles of claim 14, wherein the charged particle surface is positively charged.
 16. The stable dispersion of nanoparticles of claim 14, wherein the charged particle surface is negatively charged.
 17. The stable dispersion of nanoparticles of claim 1, wherein the nanoparticles comprise a nanoparticle that does not have a charged particle surface in the dispersion.
 18. The stable dispersion of nanoparticles of claim 1, wherein the stabilization period is 1 day, 1 week, 1 month or 1 year.
 19. The stable dispersion of nanoparticles of claim 1, wherein the nanoparticles are present in the dispersion in an amount ranging from 0.001 wt. % to 50 wt. % relative to the dispersion weight.
 20. The stable dispersion of nanoparticles of claim 1, wherein a weight ratio of the combined anionic and cationic species to the nanoparticles in the dispersion ranges from 1:10 to 10:1 combined species to nanoparticles. 